The present invention relates to a switch apparatus and, more particularly, to a switch apparatus suitable for use as a pole switch of a distribution system.
A conventional pole switch for use in a distribution system has, as disclosed in Japanese Patent Laid-Open Publication No. 61-99226, a pair of 3-phase bushings arranged on both sides of a common horizontal axis of a container, breaking portions of three phases arranged in independent insulating molds between the pair of bushings, the breaking portion of each phase having contact terminals which make and break electrical contact by movement along the above-mentioned horizontal axis, and tulip-type contactors arranged between both contact terminals and the bushings.
Thus, the known pole switch has breaking portions which are arranged between a pair of bushings and move in the axial direction so as to make and break electrical contact, so that the length of the whole switch is inevitably large in the axial direction of the bushings. Such a long pole switch requires a strong supporting structure which is quite undesirable from the viewpoint of easy and safe mounting of the switch on a pole.
Known pole switches have been designed to be incorporated in a grounding section detection system but no consideration has been taken in regard to a short-circuit section detection system. In case of a short-circuit accident, breaking of power is achieved by a breaker in a substation, so that short-circuit current flows through a pole switch only for a short period, e.g., within 1 second. Therefore, it has been unnecessary to take any protective measure for protecting a pole switch against short-circuit current. In recent years, however, there is a demand for short-circuit section detection system including pole switches of a distribution system. Such a short-circuit section detection system can be realized by applying the technique of grounding section detection system. In such a case, short-circuit current may flow in a pole switch for a comparatively long time, e.g., 3 seconds or so. Thus, a pole switch is required to withstand an electromagnetic force generated by short-circuit current flowing in the pole switch. Unfortunately, however, existing pole switches cannot withstand electromagnetic reaction force produced by a short-circuit current.